The present invention relates to a wireless local access network (WLAN), and more particularly, to a method and apparatus of transmitting a physical layer convergence protocol (PLCP) protocol data unit (PPDU) in a WLAN.
With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local access network (WLAN) is a technology whereby super high-speed Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
Ever since the institute of electrical and electronics engineers (IEEE) 802, i.e., a standardization organization for WLAN technologies, was established in February 1980, many standardization works have been conducted. In the initial WLAN technology, a frequency of 2.4 GHz was used according to the IEEE 802.11 to support a data rate of 1 to 2 Mbps by using frequency hopping, spread spectrum, infrared ray communication, etc. Recently, the WLAN technology can support a data rate of up to 54 Mbps by using orthogonal frequency division multiplex (OFDM). In addition, the IEEE 802.11 is developing or commercializing standards of various technologies such as quality of service (QoS) improvement, access point (AP) protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environments, fast roaming, mesh networks, inter-working with external networks, wireless network management, etc.
In the IEEE 802.11, the IEEE 802.11b supports a data rate of up to 11 Mbps by using a frequency band of 2.4 GHz. The IEEE 802.11a commercialized after the IEEE 802.11b uses a frequency band of 5 GHz instead of the frequency band of 2.4 GHz and thus significantly reduces influence of interference in comparison with the very congested frequency band of 2.4 GHz. In addition, the IEEE 802.11a has improved the data rate to up to 54 Mbps by using the OFDM technology. Disadvantageously, however, the IEEE 802.11a has a shorter communication distance than the IEEE 802.11b. Similarly to the IEEE 802.11b, the IEEE 802.11g realizes the data rate of up to 54 Mbps by using the frequency band of 2.4 GHz. Due to its backward compatibility, the IEEE 802.11g is drawing attention, and is advantageous over the IEEE 802.11a in terms of the communication distance.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate and throughput which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing speed of up to 540 Mbps at a frequency band of 5 GHz, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate. In addition, this standard may use a coding scheme which transmits several duplicated copies to increase data reliability and also may use the OFDM to support a higher data rate.
With the widespread use of WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing speed supported by IEEE 802.11n. However, an IEEE 802.11n medium access control (MAC)/physical layer (PHY) protocol is not effective to provide a throughput of 1 Gbps or more. This is because the IEEE 802.11n MAC/PHY protocol is designed for an operation of a single station (STA), that is, an STA having one network interface card (NIC), and thus when a frame throughput is increased while maintaining the conventional IEEE 802.11n MAC/PHY protocol, a resultant additional overhead is also increased. Consequently, there is a limitation in increasing a throughput of a wireless communication network while maintaining the conventional IEEE 802.11n MAC/PHY protocol, that is, a single STA architecture.
Therefore, to achieve a data processing speed of 1 Gbps or more in the wireless communication system, a new system different from the conventional IEEE 802.11n MAC/PHY protocol (i.e., single STA architecture) is required. A very high throughput (VHT) system is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing speed of 1 Gbps or more in a MAC service access point (SAP). The VHT system is named arbitrarily. To provide a throughput of 1 Gbps or more, a feasibility test is currently being conducted for the VHT system using 4×4 MIMO and a channel bandwidth of 80 MHz.
The IEEE 802.11a standard uses a channel bandwidth of 20 MHz at a 5 GHz band. According to this standard, up to 13 channels can be used, which may differ from one country to another. In addition, the IEEE 802.11n standard uses channel bandwidths of 20 MHz and 40 MHz at the 5 GHz band. In this situation, the newly proposed VHT system can use a channel bandwidth of 80 MHz or more at the 5 GHz band according to two methods described below.
In a first method, a channel bandwidth of 80 MHz or more is used, and a channel in use includes a plurality of non-contiguous subchannels. Subchannels are non-contiguous when a different band is allocated therebetween. The channel used in this method can be referred to as an “aggregation channel”. A plurality of 20 MHz subchannels can be grouped to ensure an 80 MHz aggregation channel required in the VHT system. Advantageously, this method can be a practical solution that considers a current channel usage at the 5 GHz band which is commercialized and realized at present. However, it is not easy to manage the non-contiguous subchannels according to a single communication protocol, and channel efficiency may differ from one subchannel to another when a subchannel spacing is great. Therefore, this method is not much effective.
In a second method, a channel in use includes a plurality of contiguous subchannels. The bandwidth of the channel may be 80 MHz or more. The channel used in this method can be referred to as a “bonding channel”. 20 MHz subchanncls contiguous to one another are grouped into 4 subchannels to ensure a 80 MHz bonding channel required in the VHT WLAN system. Since this method concurrently manages a plurality of contiguous subchannels, there is an advantage in that channel management can be effectively achieved and a channel characteristic is not significantly different from one subchannel to another.
However, the VHT system using the bonding channel can be adopted by solving a problem of coexistence with a WLAN system using the conventional 5 GHz band, that is, the IEEE 802.11a and IEEE 802.11n WLAN system. That is, if the coexistence problem with the IEEE 802.11a and IEEE 802.11n WLAN system currently commercialized is not solved, it is difficult to adopt the VHT system using a continuous channel bandwidth of 80 MHz or more at the 5 GHz band. Consequently, the VHT system using the continuous channel bandwidth of 80 MHz or more inevitably has to coexist with the conventional IEEE 802.11a and IEEE 802.11n WLAN system. Therefore, there is a need to solve the coexistence problem with the conventional WLAN system.